public ImagePlus groupZProject(ImagePlus imp, int method, int groupSize) {
if (method < 0 || method >= ZProjector.METHODS.length) return null;
imp.setDimensions(1, groupSize, imp.getStackSize() / groupSize);
ZProjector zp = new ZProjector(imp);
zp.setMethod(method);
zp.setStartSlice(1);
zp.setStopSlice(groupSize);
zp.doHyperStackProjection(true);
return zp.getProjection();
}